As a magnetic field measurement device that measures a magnetic field, one using a magneto-impedance sensor (hereinafter also referred to as “MI sensor”) is known (see Patent Document 1 as below). The MI sensor includes a magneto-sensitive body formed of an amorphous alloy, and a detection coil wound around the magneto-sensitive body. The MI sensor is configured to output a voltage corresponding to a magnetic field acting on the magneto-sensitive body from the detection coil.
If the magnetic field acting on the magneto-sensitive body is relatively weak, the output voltage of the detection coil is substantially proportional to the magnetic field. In other words, in this case, the output voltage is expressed as a linear function of the magnetic field. The magnetic field measurement device stores the slope of the linear function as a sensitivity. The magnetic field measurement device is configured to calculate the magnetic field acting on the magneto-sensitive body, using the sensitivity and the output voltage of the detection coil.